1. Field of the Invention
The invention relates to an apparatus that can detect when one or more target objects are in vicinity of their respective reference surfaces or reference objects.
The invention also relates to a detection system that can cooperate with the apparatuses and can determine when one or more target objects are in vicinity of their respective reference surfaces or reference objects.
Moreover, the invention relates to a method for determining when one or more target objects are in the vicinity of their respective reference surfaces or reference objects.
There are today several known methods for determining whether a target object is in the vicinity of a reference surface or other reference object.
Proximity detection is of interest, inter alia, in industrial, automotive and avionic systems. By means of proximity detectors the systems can report their own position relatively to reference objects and report conditions, as for example to determine the condition of valves (open, closed) provided with such proximity detectors. In automatic or autonomous systems the systems can themselves respond to the conditions of proximity detectors and other sensors, by changing speed or velocity direction, and possibly perform a series of different operations depending upon the state of the system as a whole.
In general proximity detectors have the property that there is no requirement for physical contact between the said target object and the said reference object in order to determine that the two are close to each other. In some cases it is also decisive that there is no requirement for physical contact between the detector system and one or more of the two said objects, and that proximity detection accordingly is obtained by remote sensing. It may also be decisive that the equipment on the two said objects does not require any electrical or other energy. Moreover, it can be decisive that the equipment has a low weight. Besides it may be decisive that the equipment is simple and inexpensive to manufacture. In many cases it may be important that the equipment does not require any maintenance. Furthermore it is often important that the equipment or the measuring method does not have any influence on the target object or environments, for example by disturbing electric or magnetic fields. In use of medical equipment there will be a strict requirement that the equipment does not hurt the patient. The present invention satisfies all the above aims.
2. Description of the Related Art
A number of different proximity detector principles are known, for example based on ultra sound propagation distance measurement etc. (U.S. Pat. No. 6,114,950, DE3235028, U.S. Pat. No. 5,144,593), triangulation with visible or invisible light (W09219984), optical differential phase measurement (U.S. Pat. No. 4,752,799), fibre optic sensors (U.S. Pat. No. 6,498,654), laser-based principles (DE2448898), magnetic principles (U.S. Pat. No. 6,127,821, U.S.2003173957) etc.
U.S. Pat. No. 5,200,604 describes an optical proximity detector for a probe in a laser scalpel device. The proximity detector consists of a light source, a light conductor leading the light out to an output aperture and a light detector receiving light via a light conductor to an aperture in the vicinity of the output aperture. Proximity to a reference surface is calculated from the reflected light intensity. The purpose is to avoid the activation of a laser scalpel before there is contact with the tissue in which there is to be cut.
U.S. Pat. No. 4,991,509 describes a method and an apparatus for determining the spacing between an object and a reference surface. The proximity detector consists of a light source, a light conductor leading the light out to an output aperture, and a light detector receiving light via a light conductor to an aperture in the vicinity of the output aperture. The two apertures are spaced at a certain distance from each other so that the light cone emitted overlaps to a larger or smaller degree the field of view captured by the light detector through the input aperture. Proximity to a reference surface is calculated from the reflected light intensity.
The two patents U.S. Pat. No. 5,200,604 and U.S. Pat. No. 4,991,509 describe proximity detection by means of a principle wherein source and detection have a certain mutual spacing so that the light cone from the light source and the field of view of the light detector will cover a common volume or a common area on the reference object, that will vary depending upon the spacing between the target object and the reference surface, thereby representing a varying back-scattered light intensity. In contrast to the present invention, these patents do not comprise any lenses or curved mirrors with associated focal lengths that define the proximity detection. The patents do not describe any devices wherein the light cone of the light source and the field of view of the light detector are coincident; on the contrary a specified lateral spacing is required between the two apertures so that the light cone and the light detector will have a partially overlapping coverage area that in turn depends on the distance to the reference surface and where this variable overlap area gives a varying back-scattered light intensity that can be measured in the light detector. Thus, a prerequisite in the two patents is a lateral distance between input aperture and output aperture in order that the devices shall operate properly, whereas the present invention does not involve the requirement that input aperture and output aperture shall be separated by a lateral distance.